1. Field of the Present Disclosure
The present disclosure relates to an image forming apparatus.
2. Description of the Related Art
In an image forming apparatus that includes an electrographic development system, a printing density characteristic (i.e. a characteristic of printing densities for pixel values of image data) is changed owing to aging of the development system such as a photoconductor drum.
FIG. 6 shows a diagram that explains change of a printing density characteristic due to aging of a development system.
Originally as indicated by a dashed line in FIG. 6, it is favorable that the printing density is linear to pixel values of an image to be printed. However, as indicated by a solid line in FIG. 6, gradation in a low density range and a high density range is lost owing to aging of the development system.
Some image forming apparatuses use gamma correction for restraining effect due to such change of the characteristic.
For restraining effect due to such change of the aforementioned characteristic using gamma correction, it is required to perform calibration for determining a characteristic of the gamma correction. In the calibration, patch images are developed, toner densities of the patch images are measured using a density sensor, and a characteristic of the gamma correction is determined on the basis of the measurement result.
However, it takes a long time for the calibration, and in a machine of a machine type that includes no density sensors, it is difficult to perform the calibration.